1. Field of the Invention
This invention relates to an information signal recording system for recording information signals.
2. Description of the Related Art
Various methods of recording information signals by compressing them have been developed during recent years for recording in a highly dense state such information signals that abound with information such as picture information signals. The known information signal compressing methods include a method called time-axis transformation system (hereinafter referred to as TAT system). The TAT system operates on a principle which is as shown in FIG. 1 of the accompanying drawings. Referring to FIG. 1, an original signal is divided into groups to have each contain a predetermined amount of information as indicated by broken lines. A discrimination is made between denseness and sparseness of information included in each of these groups. For a group which is determined to be dense, all the data obtained by sampling the original signal is transmitted as transmission data. For a group determined to be sparse, only a portion of all the data is transmitted as transmission data while the rest is not transmitted and is processed as thinned-out data.
Therefore, the number of data to be transmitted per unit time decreases. The transmission signal is compressed band-wise from the original signal. The information signal is thus compressed before transmission. After transmission, the signal is restored to the original state of signal on the basis of the data transmitted. In restoring the original signal, interpolation data is obtained by proximately reproducing the thinned-out data using the transmitted data. The interpolation data is positioned in place of the sparse parts and thus closely resembles the thinned-out data. Therefore, information can be transmitted without being deteriorated from its original state despite of the transmission band which is greatly compressed as compared with a band otherwise necessary for transmission of the whole data.
Each group is examined for the denseness or sparseness of information carried by the original signal in determining whether the group is to be transmitted in a whole data transmitting mode or in a partial data transmitting mode. Then, information on the result of this determination is also transmitted as a transmission mode information signal.
It is conceivable that the information-signal compression method mentioned above can be advantageously applied to magnetic recording and reproduction of compressed information signals. However, if a transmission mode information signal for determining the above-stated transmission mode either becomes erroneous or erased due to a drop-out or the like in a recording and reproducing system, it becomes no longer possible to restore the information signal to its original state. After occurrence of such an error, the information signal remains unrestorable unless the transmission mode information signal is synchronized with the transmission data. Further, in that event, since the signal reproduced remains invalid as it differs from the original signal until completion of the synchronizing process, frequent occurrence of errors in the transmission mode information signal would render the whole recorded information meaningless.